Police said it was suspected a truck was changing lanes when the couple crashed into the side of it.
However, a local news organisation noted the cause of the accident is still under investigation.
The 22-year-old was airlifted to hospital in a critical condition before dying a short time later.
Julia's stepfather, Jerônimo Onofre, told local newspaper G1 she died in the early hours of July 16.
"We were at our house, me and my wife, Julia's mother, when the hospital called with the news," he recalled.
"We got a flight and, at midnight, we were in Curitiba. She died around 1am."
Onofre said the family had to inform Daniel Cayuela his wife had died.
"He didn't know. We decided to tell him together, as a family. Daniel is in a state of shock, crying a lot, not believing what happened, they were very united and in love."
Their doomed trip was supposed to see them travel through the states of Sao Paulo, Parana and Santa Catarina.
